// Components for manipulating non-owning sequences of objects -*- C++ -*-

// Copyright (C) 2019-2020 Free Software Foundation, Inc.
//
// This file is part of the GNU ISO C++ Library.  This library is free
// software; you can redistribute it and/or modify it under the
// terms of the GNU General Public License as published by the
// Free Software Foundation; either version 3, or (at your option)
// any later version.

// This library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.

// Under Section 7 of GPL version 3, you are granted additional
// permissions described in the GCC Runtime Library Exception, version
// 3.1, as published by the Free Software Foundation.

// You should have received a copy of the GNU General Public License and
// a copy of the GCC Runtime Library Exception along with this program;
// see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
// <http://www.gnu.org/licenses/>.

/** @file span
 *  This is a Standard C++ Library header.
 */

//
// P0122 span library
// Contributed by ThePhD
//

#ifndef _GLIBCXX_SPAN
#define _GLIBCXX_SPAN 1

#pragma GCC system_header

#if __cplusplus > 201703L

#include <type_traits>
#include <array>
#include <bits/stl_iterator.h>
#include <bits/range_access.h>

#if __cpp_lib_concepts
namespace std _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION

#define __cpp_lib_span 201902L

  inline constexpr size_t dynamic_extent = static_cast<size_t>(-1);

  template<typename _Type, size_t _Extent>
    class span;

  namespace __detail
  {
    template<typename _Tp>
      struct __is_std_span : false_type { };

    template<typename _Tp, size_t _Num>
      struct __is_std_span<span<_Tp, _Num>> : true_type { };

    template<typename _Tp>
      struct __is_std_array : false_type { };

    template<typename _Tp, size_t _Num>
      struct __is_std_array<_GLIBCXX_STD_C::array<_Tp, _Num>> : true_type { };

#ifdef _GLIBCXX_DEBUG
    template<typename _Tp, size_t _Num>
      struct __is_std_array<__debug::array<_Tp, _Num>> : true_type { };
#endif

    template<size_t _Extent>
      class __extent_storage
      {
      public:
	constexpr
	__extent_storage(size_t) noexcept
	{ }

	static constexpr size_t
	_M_extent() noexcept
	{ return _Extent; }
      };

    template<>
      class __extent_storage<dynamic_extent>
      {
      public:
	constexpr
	__extent_storage(size_t __extent) noexcept
	: _M_extent_value(__extent)
	{ }

	constexpr size_t
	_M_extent() const noexcept
	{ return this->_M_extent_value; }

      private:
	size_t _M_extent_value;
      };
  } // namespace __detail

  template<typename _Type, size_t _Extent = dynamic_extent>
    class span
    {
      template<size_t _Offset, size_t _Count>
	static constexpr size_t
	_S_subspan_extent()
	{
	  if constexpr (_Count != dynamic_extent)
	    return _Count;
	  else if constexpr (extent != dynamic_extent)
	    return _Extent - _Offset;
	  else
	    return dynamic_extent;
	}

      // _GLIBCXX_RESOLVE_LIB_DEFECTS
      // 3255. span's array constructor is too strict
      template<typename _Tp, size_t _ArrayExtent>
	using __is_compatible_array = __and_<
	  bool_constant<(_Extent == dynamic_extent || _ArrayExtent == _Extent)>,
	  __is_array_convertible<_Type, _Tp>>;

      template<typename _Iter, typename _Ref = iter_reference_t<_Iter>>
	using __is_compatible_iterator = __and_<
	  bool_constant<contiguous_iterator<_Iter>>,
	  is_lvalue_reference<iter_reference_t<_Iter>>,
	  is_same<iter_value_t<_Iter>, remove_cvref_t<_Ref>>,
	  __is_array_convertible<_Type, remove_reference_t<_Ref>>>;

      template<typename _Range>
	using __is_compatible_range
	  = __is_compatible_iterator<ranges::iterator_t<_Range>>;

    public:
      // member types
      using value_type             = remove_cv_t<_Type>;
      using element_type           = _Type;
      using size_type              = size_t;
      using reference              = element_type&;
      using const_reference        = const element_type&;
      using pointer                = _Type*;
      using const_pointer          = const _Type*;
      using iterator
	= __gnu_cxx::__normal_iterator<pointer, span>;
      using const_iterator
	= __gnu_cxx::__normal_iterator<const_pointer, span>;
      using reverse_iterator       = std::reverse_iterator<iterator>;
      using const_reverse_iterator = std::reverse_iterator<const_iterator>;
      using difference_type        = ptrdiff_t;

      // member constants
      static inline constexpr size_t extent = _Extent;

      // constructors

      constexpr
      span() noexcept
      requires ((_Extent + 1u) <= 1u)
      : _M_extent(0), _M_ptr(nullptr)
      { }

      constexpr
      span(const span&) noexcept = default;

      template<typename _Tp, size_t _ArrayExtent>
	requires (__is_compatible_array<_Tp, _ArrayExtent>::value)
	constexpr
	span(_Tp (&__arr)[_ArrayExtent]) noexcept
	: span(static_cast<pointer>(__arr), _ArrayExtent)
	{ }

      template<typename _Tp, size_t _ArrayExtent>
	requires (__is_compatible_array<_Tp, _ArrayExtent>::value)
	constexpr
	span(array<_Tp, _ArrayExtent>& __arr) noexcept
	: span(static_cast<pointer>(__arr.data()), _ArrayExtent)
	{ }

      template<typename _Tp, size_t _ArrayExtent>
	  requires (__is_compatible_array<const _Tp, _ArrayExtent>::value)
	constexpr
	span(const array<_Tp, _ArrayExtent>& __arr) noexcept
	: span(static_cast<pointer>(__arr.data()), _ArrayExtent)
	{ }

    public:
      template<ranges::contiguous_range _Range>
	requires (_Extent == dynamic_extent)
	  && (!__detail::__is_std_span<remove_cvref_t<_Range>>::value)
	  && (!__detail::__is_std_array<remove_cvref_t<_Range>>::value)
	  && (!is_array_v<remove_reference_t<_Range>>)
	  && (__is_compatible_range<_Range>::value)
	constexpr
	span(_Range&& __range)
	noexcept(noexcept(ranges::data(__range))
		  && noexcept(ranges::size(__range)))
	: span(ranges::data(__range), ranges::size(__range))
	{ }

      template<contiguous_iterator _ContiguousIterator,
	sized_sentinel_for<_ContiguousIterator> _Sentinel>
	  requires (__is_compatible_iterator<_ContiguousIterator>::value)
	    && (!is_convertible_v<_Sentinel, size_type>)
	constexpr
	span(_ContiguousIterator __first, _Sentinel __last)
	noexcept(noexcept(__last - __first))
	: _M_extent(static_cast<size_type>(__last - __first)),
	  _M_ptr(std::to_address(__first))
	{
	  if (_Extent != dynamic_extent)
	    __glibcxx_assert((__last - __first) == _Extent);
	}

      template<contiguous_iterator _ContiguousIterator>
	requires (__is_compatible_iterator<_ContiguousIterator>::value)
	constexpr
	span(_ContiguousIterator __first, size_type __count)
	noexcept
	: _M_extent(__count), _M_ptr(std::to_address(__first))
	{ __glibcxx_assert(_Extent == dynamic_extent || __count == _Extent); }

      template<typename _OType, size_t _OExtent>
	requires (_Extent == dynamic_extent || _Extent == _OExtent)
	  && (__is_array_convertible<_Type, _OType>::value)
	constexpr
	span(const span<_OType, _OExtent>& __s) noexcept
	: _M_extent(__s.size()), _M_ptr(__s.data())
	{ }

      // assignment

      constexpr span&
      operator=(const span&) noexcept = default;

      // observers

      constexpr size_type
      size() const noexcept
      { return this->_M_extent._M_extent(); }

      constexpr size_type
      size_bytes() const noexcept
      { return this->_M_extent._M_extent() * sizeof(element_type); }

      [[nodiscard]] constexpr bool
      empty() const noexcept
      { return size() == 0; }

      // element access

      constexpr reference
      front() const noexcept
      {
	static_assert(extent != 0);
	__glibcxx_assert(!empty());
	return *this->_M_ptr;
      }

      constexpr reference
      back() const noexcept
      {
	static_assert(extent != 0);
	__glibcxx_assert(!empty());
	return *(this->_M_ptr + (size() - 1));
      }

      constexpr reference
      operator[](size_type __idx) const noexcept
      {
	static_assert(extent != 0);
	__glibcxx_assert(__idx < size());
	return *(this->_M_ptr + __idx);
      }

      constexpr pointer
      data() const noexcept
      { return this->_M_ptr; }

      // iterator support

      constexpr iterator
      begin() const noexcept
      { return iterator(this->_M_ptr); }

      constexpr const_iterator
      cbegin() const noexcept
      { return const_iterator(this->_M_ptr); }

      constexpr iterator
      end() const noexcept
      { return iterator(this->_M_ptr + this->size()); }

      constexpr const_iterator
      cend() const noexcept
      { return const_iterator(this->_M_ptr + this->size()); }

      constexpr reverse_iterator
      rbegin() const noexcept
      { return reverse_iterator(this->end()); }

      constexpr const_reverse_iterator
      crbegin() const noexcept
      { return const_reverse_iterator(this->cend()); }

      constexpr reverse_iterator
      rend() const noexcept
      { return reverse_iterator(this->begin()); }

      constexpr const_reverse_iterator
      crend() const noexcept
      { return const_reverse_iterator(this->cbegin()); }

      // subviews

      template<size_t _Count>
	constexpr span<element_type, _Count>
	first() const noexcept
	{
	  if constexpr (_Extent == dynamic_extent)
	    __glibcxx_assert(_Count <= size());
	  else
	    static_assert(_Count <= extent);
	  return { this->data(), _Count };
	}

      constexpr span<element_type, dynamic_extent>
      first(size_type __count) const noexcept
      {
	__glibcxx_assert(__count <= size());
	return { this->data(), __count };
      }

      template<size_t _Count>
	constexpr span<element_type, _Count>
	last() const noexcept
	{
	  if constexpr (_Extent == dynamic_extent)
	    __glibcxx_assert(_Count <= size());
	  else
	    static_assert(_Count <= extent);
	  return { this->data() + (this->size() - _Count), _Count };
	}

      constexpr span<element_type, dynamic_extent>
      last(size_type __count) const noexcept
      {
	__glibcxx_assert(__count <= size());
	return { this->data() + (this->size() - __count), __count };
      }

      template<size_t _Offset, size_t _Count = dynamic_extent>
	constexpr auto
	subspan() const noexcept
	-> span<element_type, _S_subspan_extent<_Offset, _Count>()>
	{
	  if constexpr (_Extent == dynamic_extent)
	    __glibcxx_assert(_Offset <= size());
	  else
	    static_assert(_Offset <= extent);

	  if constexpr (_Count == dynamic_extent)
	    return { this->data() + _Offset, this->size() - _Offset };
	  else
	    {
	      if constexpr (_Extent == dynamic_extent)
		{
		  __glibcxx_assert(_Count <= size());
		  __glibcxx_assert(_Count <= (size() - _Offset));
		}
	      else
		{
		  static_assert(_Count <= extent);
		  static_assert(_Count <= (extent - _Offset));
		}
	      return { this->data() + _Offset, _Count };
	    }
	}

      constexpr span<element_type, dynamic_extent>
      subspan(size_type __offset, size_type __count = dynamic_extent) const
      noexcept
      {
	__glibcxx_assert(__offset <= size());
	if (__count == dynamic_extent)
	  __count = this->size() - __offset;
	else
	  {
	    __glibcxx_assert(__count <= size());
	    __glibcxx_assert(__offset + __count <= size());
	  }
	return {this->data() + __offset, __count};
      }

    private:
      [[no_unique_address]] __detail::__extent_storage<extent> _M_extent;
      pointer _M_ptr;
    };

  // deduction guides
  template<typename _Type, size_t _ArrayExtent>
    span(_Type(&)[_ArrayExtent]) -> span<_Type, _ArrayExtent>;

  template<typename _Type, size_t _ArrayExtent>
    span(array<_Type, _ArrayExtent>&) -> span<_Type, _ArrayExtent>;

  template<typename _Type, size_t _ArrayExtent>
    span(const array<_Type, _ArrayExtent>&)
      -> span<const _Type, _ArrayExtent>;

  template<contiguous_iterator _Iter, typename _Sentinel>
    span(_Iter, _Sentinel)
      -> span<remove_reference_t<ranges::range_reference_t<_Iter>>>;

  template<typename _Range>
    span(_Range &&)
      -> span<remove_reference_t<ranges::range_reference_t<_Range&>>>;

  template<typename _Type, size_t _Extent>
    inline
    span<const byte, _Extent == dynamic_extent
	? dynamic_extent : _Extent * sizeof(_Type)>
    as_bytes(span<_Type, _Extent> __sp) noexcept
    {
      return {reinterpret_cast<const byte*>(__sp.data()), __sp.size_bytes()};
    }

  template<typename _Type, size_t _Extent>
    inline
    span<byte, _Extent == dynamic_extent
       ? dynamic_extent : _Extent * sizeof(_Type)>
    as_writable_bytes(span<_Type, _Extent> __sp) noexcept
    {
      return {reinterpret_cast<byte*>(__sp.data()), __sp.size_bytes()};
    }

  // tuple helpers
  template<size_t _Index, typename _Type, size_t _Extent>
    constexpr _Type&
    get(span<_Type, _Extent> __sp) noexcept
    {
      static_assert(_Extent != dynamic_extent && _Index < _Extent,
	"get<I> can only be used with a span of non-dynamic (fixed) extent");
      return __sp[_Index];
    }

  template<typename _Tp> struct tuple_size;
  template<size_t __i, typename _Tp> struct tuple_element;

  template<typename _Type, size_t _Extent>
    struct tuple_size<span<_Type, _Extent>>
    : public integral_constant<size_t, _Extent>
    {
      static_assert(_Extent != dynamic_extent, "tuple_size can only "
	"be used with a span of non-dynamic (fixed) extent");
    };

  template<size_t _Index, typename _Type, size_t _Extent>
    struct tuple_element<_Index, span<_Type, _Extent>>
    {
      static_assert(_Extent != dynamic_extent, "tuple_element can only "
	"be used with a span of non-dynamic (fixed) extent");
      static_assert(_Index < _Extent, "Index is less than Extent");
      using type = _Type;
    };

  namespace ranges
  {
    template<typename> extern inline const bool enable_safe_range;
    // Opt-in to safe_range concept
    template<typename _ElementType, size_t _Extent>
      inline constexpr bool
	enable_safe_range<span<_ElementType, _Extent>> = true;
  }
_GLIBCXX_END_NAMESPACE_VERSION
} // namespace std
#endif // concepts
#endif // C++20
#endif // _GLIBCXX_SPAN
